(1) Field of the Invention
The present invention relates generally to a system and method for communicating data between terminals applicable to automotive vehicles.
(2) Background art
Various kinds of systems and methods for communicating data between terminals applicable to automotive vehicles have been proposed in which the information related to operations of a multiple number of operation portions is transmitted in a multiplex transmission mode via a fewer number of connection lines.
Such types of data communication systems are exemplified by U.S. Pat. Nos. 4,809,266 issued on Feb. 28, 1989, 4,926,417 issued on May 15, 1990, and 4,821,262 issued on Apr. 11, 1989.
Another previously proposed multiplex communication system will be explained below.
A vehicle is constituted, for example, by an engine compartment portion, dash board portion, instrument panel portion, and trunk portion. A first multiplex transmission module is installed on the engine compartment portion. A second multiplex transmission module is installed on the dash board portion. A third multiplex transmission module is installed on the instrument panel portion. A fourth multiplex transmission module is installed on the trunk portion.
The first multiplex transmission module is connected to a multiplex transmission line and switch load supply line. The second multiplex transmission module controls a vehicle lamp group in accordance with control data and is also connected to the multiplex transmission line. The first multiplex transmission module controls a front vehicle lamp group. Signal groups are transmitted from front vehicle lamps as well as an AT (automatic transmission) position switch group and an AT shift sensor group, the signals from these groups being superposed on the multiplex transmission line.
In the same way, the second multiplex transmission module controls the vehicle lamp group from control data derived from a plurality of switches and dash board peripheral switch groups installed on peripherals of the dash board portion.
The third multiplex transmission module installed on the instrument panel portion controls the instrument lamp group constituted by a plurality of lamps.
The fourth multiplex transmission module installed on the trunk portion controls rear vehicle lamp group.
In the previously proposed multiplex transmission system, a single multiplex transmission module installed on, e.g., the engine compartment portion, controls the lamp group at both sides of the vehicle, i.e., right front lamp group and left front lamp group. Therefore, if trouble occurs in the multiplex transmission module, both right and left front lamps cannot operate.
If separate multiple transmission modules to control the right and left front lamp groups are installed so that each front lamp groups can independently be controlled, the above drawback can be overcome.
In another previously proposed system, separate multiple transmission modules are installed for groups of terminals present at the left side and the right side of the vehicle. Further, these multiple transmission modules are located in a common housing with their respective terminals. Therefore, a number of connection lines between the terminals and operation portions, i.e., the number of (connector) harnesses, can be reduced.
Even if trouble occurs in one of the multiple transmission modules present at the left side of the vehicle in a pair of multiple transmission modules corresponding to terminals present at the left side and at the right side of the vehicle as described above, operation of the other multiple transmission module can be maintained.
However, in such a previously proposed multiplex communication system as described above, the number of multiplex transmission modules (which are configured as slave stations linked to a master station) are increased and sequential polling is carried out for the slave stations according to a calling order previously set so that communication between the master station and a selected slave station is carried out according to the calling order. Hence, a predetermined time is required for the master station to poll all of the slave stations, the polling cycle terminating with the last station according to the calling order. Therefore, a time delay often occurs between a time when an operator operates a particular operation portion until the time when the corresponding terminal is activated.
For example, assuming there are ten slave stations to be called in a given calling cycle. Referring to FIG. 4(a) a slave station 100 is associated with a headlamp switch, a slave station 200 being associated with a left headlamp and a slave station 600 associated with a right headlamp. When the head lamp switch associated with the first slave station 100, (called at a time T.sub.0), is operated at a time T.sub.1 after the first slave station has been called, the information from the head lamp switch will not be recognized until the station is called again in the subsequent calling cycle. That is to say, at a time T.sub.10 (the beginning of the next calling cycle), the information that the light switch 100 has been operated will be present in the system. After the information is received by the terminal the head lamp arranged on a front left side of the vehicle will be operated, becoming ON when the slave station 200 is called at the time T.sub.11. The right headlamp will not be operated until the slave station 600 for the front right headlamp is called at a time T.sub.16. Hence, at a time T.sub.17 when the callings to all appropriate slave stations is ended, the illumination of the pair of left and right headlamps is completed. Hence, in a case where a data time T.sub.f of the system data format is set at, e.g., 3.5 milliseconds, a response delay time of 3.5 ms occurs between each slave station from the time T.sub.1 to T.sub.17 (refer to FIG. 4) causing considerable delay to occur between the operation of the left headlamp and that of the right headlamp.
In addition, e.g., in a case where a hazard switch is operated to indicate an emergency condition, or to caution other drivers that the vehicle is stopped, it is necessary to simultaneously operate signal lamps arranged on the front right and front left sides of the vehicle so as to blink at a regular frequency. In such a case, if a delay occurs between a time when the multiplex transmission module which governs the terminal group arranged on the front left side of the vehicle is called and a time when the multiplex transmission module which governs the terminal group arranged on the front right side of the vehicle is called, the signal lamps arranged on each side of the vehicle cannot blink simultaneously. Therefore, further improvement is required.